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workqueue: defer the worker wakeup outside pool->lock in __queue_work()

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__queue_work() is the enqueue hot path: it inserts the work item and
calls kick_pool() while holding pool->lock. kick_pool() ends in a
wakeup, which takes the target task's rq->lock, so rq->lock nests under
pool->lock on every enqueue that wakes a worker on a contended unbound
pool.

Use kick_pool_pick() to select and claim the worker under pool->lock and
issue the wakeup with wake_up_process() right after dropping the lock.

Signed-off-by: Breno Leitao <leitao@debian.org>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Breno Leitao 2026-06-26 02:57:54 -07:00 committed by Tejun Heo
parent 1ad5dcee7c
commit d070f2916a
1 changed files with 4 additions and 1 deletions
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5
kernel/workqueue.c
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@ -2302,6 +2302,7 @@ static void __queue_work(int cpu, struct workqueue_struct *wq,
{
struct pool_workqueue *pwq;
struct worker_pool *last_pool, *pool;
struct task_struct *wake_task = NULL;
unsigned int work_flags;
unsigned int req_cpu = cpu;
@ -2424,7 +2425,7 @@ static void __queue_work(int cpu, struct workqueue_struct *wq,
trace_workqueue_activate_work(work);
insert_work(pwq, work, &pool->worklist, work_flags);
kick_pool(pool);
kick_pool_pick(pool, &wake_task);
} else {
work_flags |= WORK_STRUCT_INACTIVE;
insert_work(pwq, work, &pwq->inactive_works, work_flags);
@ -2432,6 +2433,8 @@ static void __queue_work(int cpu, struct workqueue_struct *wq,
out:
raw_spin_unlock(&pool->lock);
if (wake_task)
wake_up_process(wake_task);
rcu_read_unlock();
}